The present invention relates to a control valve for a variable displacement compressor that is used in a refrigerant circuit of a vehicle air conditioner.
FIG. 5 illustrates a part of a control valve disclosed in Japanese Unexamined Patent Publication No. 11-324930. In this control valve, two pressure monitoring points P1, P2 are located in a refrigerant circuit. The pressure difference between the two points monitoring P1, P2 is mechanically detected by a pressure sensing member 101. The position of a valve body 102 is determined in accordance with a force generated based on the pressure difference. The pressure in a control chamber (for example, the crank chamber of a swash plate type compressor) is adjusted according to the position of the valve body 102.
The pressure difference between the pressure monitoring points P1, P2 represents the flow rate of refrigerant in the refrigerant circuit. The pressure sensing member 101 determines the position of the valve body 102 such that the displacement of the compressor is changed to cancel the fluctuation of the pressure difference, or the fluctuation of the refrigerant flow rate in the refrigerant circuit.
The above described control valve has a simple internal self-control function for maintaining a predetermined single refrigerant flow rate. In other words, the control valve does not actively change the refrigerant flow rate, and therefore, cannot respond to subtle changes in demand for controlling the air conditioning.
Accordingly, it is an objective of the present invention to provide a control valve for a variable displacement compressor that accurately controls air conditioning.
To achieve the foregoing and other objectives and in accordance with the purpose of the present invention, a control valve used for a variable displacement compressor installed in a refrigerant circuit is provided. The compressor varies the displacement in accordance with the pressure in a control chamber. The compressor has a control passage, which connects the control chamber to a pressure zone in which the pressure is different from the pressure of the control chamber. The control valve includes a valve housing, a valve chamber defined in the valve housing, a valve body, a pressure sensing chamber defined in the valve housing, a pressure sensing member, a pressure sensing rod, a solenoid chamber, a movable iron core, a stationary iron core, a solenoid rod, and an electromagnetic actuator. The valve body is accommodated in the valve chamber for adjusting the opening degree of the control passage. The pressure sensing member divides the pressure sensing chamber into a first pressure chamber and a second pressure chamber. The pressure at a first pressure monitoring point in the refrigerant circuit is applied to the first pressure chamber. The pressure at a second pressure monitoring point in the refrigerant circuit, which is downstream of the first pressure monitoring point, is applied to the second pressure chamber. The pressure sensing rod is slidably supported by the valve housing between the valve chamber and the pressure sensing chamber. An end of the pressure sensing rod is connected to the pressure sensing member and the other end of the pressure sensing rod contacts the valve body. The pressure sensing member moves the valve body via the pressure sensing rod in accordance with the pressure difference between the first pressure chamber and the second pressure chamber such that the displacement of the compressor is varied to counter changes of the pressure difference. The solenoid chamber is defined in the valve housing to be adjacent to the valve chamber. The movable iron core is movably accommodated in the solenoid chamber. The stationary iron core is located between the valve chamber and the solenoid chamber. The stationary iron core separates the valve chamber from the solenoid chamber. The solenoid rod extends through and is slidably supported by the stationary iron core. The solenoid rod supports the valve body in the valve chamber and supports the movable iron core in the solenoid chamber. The electromagnetic actuator applies an urging force to the pressure sensing member in accordance with an external command. The electromagnetic actuator includes the movable iron core and the stationary iron core. The urging force applied to the pressure sensing member by the actuator corresponds to a target value of the pressure difference. The pressure sensing member moves the valve body such that the pressure difference seeks the target value.
Other aspects and advantages of the invention will become apparent from the following description, taken in conjunction with the accompanying drawings, illustrating by way of example the principles of the invention.